Last week, my husband fainted while urinating. His doctor said he might have micturition syncope. What causes this, and what can he do about it?

Answers from Phillip A. Low, M.D.

Micturition (or post-micturition) syncope is fainting during or, more commonly, immediately after urination due to a severe drop in blood pressure. Micturition syncope is most common in older men and usually occurs at night after a deep sleep.

The exact cause of micturition syncope isn't fully understood. But it may be related to opening (vasodilation) of the blood vessels that occurs when getting up and standing at the toilet or that occurs at the rapid emptying of a full bladder. This is thought to result in a sudden drop in blood pressure.

Other factors that may play a role in micturition syncope include:

Alcohol

Hunger

Fatigue

Dehydration

Medical conditions, such as a respiratory infection

Use of alpha blockers to improve urination in men with prostate problems

Preventing micturition syncope

Micturition syncope is uncommon and should be evaluated by a doctor because it may indicate an underlying medical condition. Prevention of micturition syncope depends on recognizing the factors that contribute to micturition syncope and avoiding them.

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